Inaccurate mileage

Car ownership is an expensive proposition, and car buyers often search out the best deal for auto insurance, maintenance fees and mileage. In the case of mileage numbers, however, consumers may have gotten a raw deal from automakers. Over the past few weeks, investigations have revealed significant differences between the estimated fuel economy carmakers claimed for their vehicles and plausible real-world results.

Problems hit the US
November got off to a rocky start for automakers when the U.S. government levied a combined $300 million penalty against Hyundai Motors and Kia Motors, The New York Times reported. The fine was a response to Hyundai and Kia overstating mileage numbers for over 1 million vehicles in the U.S. The companies admitted their wrongdoing in 2012, but it's only now that the Environmental Protection Agency has doled out a punishment.

While one-third of the $300 million must be paid directly to the government, the remaining $200 million represents tax credits that Hyundai and Kia will have to forfeit. As part of the EPA's effort to cut down on greenhouse gas emissions, the agency awards tax breaks to auto manufacturers who produce cars that undercut the minimum mileage required by law. By overstating their vehicles' fuel efficiency by an average of six miles per gallon, Hyundai and Kia were able to to claim tax credits they did not actually deserve.

While Hyundai and Kia said that the incorrect numbers were the result of a procedural error and did not represent an intention to mislead customers, they made mileage statistics a cornerstone of their marketing campaigns for several vehicles. Even when mileage tests are carried out correctly, the results can often be wildly inaccurate for potential buyers.

Europe highlights problems with testing
As American regulators nailed Hyundai and Kia for their poor fuel economy reporting, the European organization Transport & Environment released a report that highlighted the dramatic difference between advertised fuel economy and real-world results. Reviewing the data, it discovered a gap of more than 30 percent between what carmakers report from environmental testing and what car​ buyers see in actual use. While this number is not directly transferrable to the U.S., which features different methods for fuel-economy testing, it highlights the difficulty inherent to fuel-efficiency tests.

While U.S. fuel-economy tests were revamped in 2009, they continue to have difficulty dealing with newer vehicles, Car and Driver reported. While the new tests are relatively accurate when reporting on traditional gas-powered vehicles, new models with hybrid power trains do not fit into the current testing model. In some cases, like Chevrolet's Volt, the vehicle will run on electric power until its batteries are depleted. Then, it switches to a gas engine. In this model, average fuel economy is nearly impossible to predict, as gas consumption is almost entirely reliant on the distance a user drives.

Why accurate mileage numbers matter
Outside of government programs to enforce fuel efficiency for environmental reasons, fuel economy is a crucial tool for consumers as they evaluate the actual cost of a car. The majority of car buyers in a Consumer Reports survey said that they want their next vehicles to have better fuel economy than their current cars. With fuel economy as a strong motivator for purchasers, automakers have a huge incentive to present their cars as having excellent fuel economy. While fuel-economy testing in the U.S. has improved, it is still not a wholly accurate predictor of actual results. The news from Europe and the increasing prevalence of cars with difficult-to-test alternative powertrains means that there is still more work to be done when evaluating fuel economy.

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